Comparative morphology of interstitial cells of Cajal: ultrastructural characterization.

The shape, distribution, and ultrastructural features of interstitial cells of Cajal (ICC) of different tissue layers and organs of the rat and guinea-pig digestive tract were described and compared with the corresponding cells in other species including mice, dogs, and humans, as reported in the literature. By light microscopy, the best marker for ICC appeared to be immunoreactivity for c-Kit. Ultrastructurally, ICC were characterized by the presence of many mitochondria, bundles of intermediate filaments, and gap junctions, which linked ICC with each other. However, ICC were morphologically heterogeneous and had particular features, depending on their tissue and organ location and species. ICC in the deep muscular plexus of the small intestine and in the submuscular plexus of the colon were the most like smooth muscle cells, and had a distinct basal lamina and numerous caveolae. In contrast, ICC of Auerbach's plexus at all levels of the gastrointestinal tract were the least like smooth muscle cells. They most closely resembled unremarkable fibroblasts. ICC within the circular muscle layer were intermediate in form. In addition to the tissue specificity, some organ and species specificity could be distinguished. The structural differences between ICC may be determined by their microenvironment, including the effects of mechanical force, type of nerve supply, and spacial relationship with smooth muscle cells.